Abstract: Objective: This study was conducted to investigate the oral safety and gut microbiota regulatory effect of cellulose nanocrystals (CNC) prepared by sulfuric acid hydrolysis (S-CNC) or phosphoric acid hydrolysis (P-CNC). Methods: Mice were divided into three groups (24 mice per group, half from each gender): control, S-CNC and P-CNC. The changes in activity behavior, body mass, body composition, organ indexes and serum biochemical indexes were examined after gavage, and pathomorphological changes in various internal organs were observed by hematoxylin-eosin (HE) staining. Feces were collected for 16S rDNA gene high-throughput sequencing to analyze the effects of S-CNC and P-CNC on the gut microbiota of mice. Results: Compared with the control group, no significant differences were observed in activity behavior, body mass, fat, fluid, lean components or organ indexes in the S-CNC and P-CNC groups (P > 0.05). The serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), uric acid (UA) and urea were unaffected by S-CNC and P-CNC administration. HE staining showed that neither CNC treatment exhibited morphological abnormalities in the major organs. S-CNC and P-CNC changed the abundance and uniformity of gut microbiota in normal mice as well as the composition of gut microbiota at the phylum, family and genus levels. S-CNC increased the relative abundance of Firmicutes in female mice, but decreased the relative abundance of Firmicutes in male mice and the relative abundance of Bacteroidetes in both male and female mice. P-CNC increased the relative abundance of Firmicutes in female mice and Bacteroidetes in male mice, but decreased the relative abundance of Firmicutes in male mice and the relative abundance of Bacteroidetes in female mice. At the family level, the relative abundance of Akkermansiaceae and Planococcaceae in the intestinal tracts of female and male mice increased after administration of S-CNC and P-CNC. Genus level analysis showed that S-CNC administration increased the relative abundance of Akkermansia and Faecalibaculum in male mice and the relative abundance of Acinetobacter in the gut of female mice. After administration of P-CNC, the relative abundance of Kurthia and Akkermansia increased in female mice, while the relative abundance of Candida decreased in male mice. Conclusion: S-CNC and P-CNC are safe for mice to eat. Moreover, both of them have a regulatory effect on the gut microbiota in mice.

Key words: cellulose nanocrystals; safety; gut microbiota; sulfuric acid hydrolysis; phosphoric acid hydrolysis